1. Field of the Invention
The present invention relates to a recording tape cartridge for rotatably accommodating a reel on which a recording tape is wound.
2. Description of the Related Art
In a conventionally known type of recording tape cartridge for a recording medium for use as an external storage device of a computer or the like, a single reel, on which a recording tape such as a magnetic tape is wound, is rotatably accommodated in the recording tape cartridge.
A magnetic tape is used, for example, for storing computer data. The tape cartridge is structured so as to prevent the magnetic tape, which may contain important information, from jamming or the like, and from being unwound unintentionally when not in use, such as during storage or the like.
The reel comprises a reel hub and upper and lower flanges, which are disposed at both ends of the reel hub. As shown in FIG. 29, a reel hub 500 and a lower flange 502 are integrally molded and, after the molding, an upper flange 504 is welded to the reel hub 500 to form a reel 506.
A magnetic tape can be wound on the reel hub 500, and width-directional end portions of the wound-on magnetic tape are retained by the upper and lower flanges 504 and 502.
As shown in FIGS. 29 and 30, the reel hub 500 is provided with a driven gear 508, which meshes with a driving gear for transmitting driving force from a drive-side driving device (not shown).
At an inner side of the driven gear 508 is disposed a metal plate 510 for magnetic attachment. The metal plate 510 is magnetically attracted by a magnet disposed at the drive-side driving device, thus preventing misalignment of the axis and keeping the meshing state of the driven gear 508 and the driving gear. However, because the reel hub 500 is provided with the driven gear 508, the metal plate 510, and the like, variations of pressure during the molding may affect the lower flange 502 molded integrally with the reel hub 500, reducing flatness of the lower flange 502, and this may be a cause of surface-runout in the drive. Further, because the flatness of the lower flange 502 is lowered, roundness of the reel hub 500 deteriorates.
The metal plate 510 is integrally molded with the reel hub 500 and the lower flange 502 inside a metal mold which molds the reel hub 500 and the lower flange 502. Three through-holes 512 for joining the metal plate 510 to the reel hub 500 are formed at regular intervals in the metal plate 510 on a concentric circle thereof. During molding, a molding material flows into the through-holes 512 to fix the metal plate 510 to the reel hub 500.
In the metal mold, a position corresponding to an inner circumferential portion of the reel hub 500 is a gate position. When the reel hub 500 and the lower flange 502 are molded, the molding material flows in a space defined by the metal mold from the position corresponding to the inner circumferential portion of the reel hub 500 towards positions corresponding to a distal portion of the reel hub 500, and in radial directions towards positions corresponding to an outer circumferential portion of the lower flange 502.
When the molding material flows into the through-holes 512 formed in the metal plate 510, air in the through-holes 512 causes friction that resists the molding material. Therefore, comparing with a case in which the molding material flows around the metal plate 510, the pressure is increased. This causes variations in the pressure in a cavity 516, and disturbs stress balance.
Because the stress balance is disturbed when the molding material is filled, the disturbed stress balance is manifested as residual stress after the molding, and causes deformation of the reel hub 500 and the lower flange 502 shown in FIG. 29. Therefore, there is a risk of lowering the accuracy of the reel hub 500 and the driven gear 508, and the flatness of the lower flange 502.
Further, as shown in FIG. 31, because within the through-hole 512 (shown by arrows) moves during hardening of the molding material, wrinkles 518 are produced. Particularly, if the wrinkles 518 produce differences in the level of the outer circumferential surface of the reel hub 500 (see FIG. 29), a winding state of the magnetic tape on the reel may be disturbed, and magnetic surfaces at the inner and outer circumferential sides of the magnetic tape may be scratched by the tape""s edges.
In view of the aforementioned, an object of the present invention is to provide a recording tape cartridge comprising a highly accurate reel including highly flat flanges. Further, there is a demand for improving breaking power of the reel.
In a first aspect of the present invention, a single reel, on which a recording tape is wound, is rotatably accommodated in a recording tape cartridge. The reel includes a hollow hub on which the recording tape is wound. Annular flanges are disposed at both ends of the hub for holding width-directional ends of the recording tape wound on the hub. Also, a metal plate is inserted at one end of the hub.
The hub is formed such that cross-sections taken radially from an axis thereof are the same as each other. This makes flowing states of a molding material the same for the respective cross-sectional directions. Therefore, the flowing state of the molding material does not differ with circumferential position.
In the first aspect of the present invention, an annular joining device that joins to an outer circumference of the metal plate may be provided at the hub. By joining the outer circumference of the metal plate inserted at the end of the hub using the annular joining device, cross-sections of the hub, taken radially from the axis thereof, can be made the same as each other.
Further, since there is no need to provide a hole or the like in the metal plate, variations in the pressure of the molding material flowing over the metal plate are small. Therefore, residual stress can be reduced, thereby improving accuracy of the hub and flatness of the flange.
Furthermore, by joining the metal plate firmly at the outer circumference thereof, the internal dimensions of a portion for joining the metal plate is increased compared with the case in which the metal plate is provided with holes. This means air is easier to remove and less likely to stay. Thus, no wrinkles are created on the hub and the flange.
In the first aspect of the present invention, the joining device may include a joining portion provided at the end of the hub. The joining portion surrounds an annular joined portion extending from an entire outer circumference of the metal plate, and joins the same.
In the present invention, the joining portion may be an annular pawl portion that holds the joined portion. By provision of the pawl portion, the metal plate is prevented from coming off.
In the present invention, the joined portion may join by projecting toward a side away from the pawl portion and meshing with the hub. Thus, the metal plate is firmly fixed to the hub.
In the present invention, an annular fitting portion can be provided in a metal mold for molding the hub, and an annular fitting portion, which fits to the fitting portion of the mold can be formed at the metal plate. Thus, the metal plate is assuredly fixed in the metal mold.
In a second aspect of the present invention, a recording tape cartridge rotatably accommodates a reel on which a recording tape is wound, and the reel includes a hollow hub on which the recording tape is wound. Flanges are welded at both ends of the hub, and the flanges retain the width-directional ends of the recording tape that is wound on the hub.
Specifically, the hub and the flanges are separately molded, and the flanges are then welded at the both ends of the hub to form the reel. Separately molding the hub and the flanges allows selection of a suitable gating system, for example disc gates, and setting of optimal molding conditions for each shape.
Therefore, compared with the case in which the hub and the flange are integrally molded, variations in pressure of the hub can be reduced and flatness of the flanges can be improved. Further, roundness of the hub can be improved by the improvement in the flatness of the flange.
Moreover, by welding the hub and the flange, they can be united with greater certainty and less backlash compared with the case in which a flange and hub are provided with pawl portions for fitting to each other, and can be united more simply compared with the case in which a flange and hub are threaded and screwed together.
In the second aspect of the present invention, a first weld boss may be provided projecting from a welding surface, for welding to the flange, along a circumferential direction of a collar provided at an outer circumferential surface of the hub. A second weld boss may be provided projecting from another welding surface, for welding to the other flange, along a circumferential direction of a stepped portion provided at an inner circumferential surface of the hub.
By providing the first weld boss and the second weld boss projecting from the welding surfaces, the weld bosses can be fused to weld the flanges to the hub when frictional heat is generated between the flanges and the hub by vibrational energy from an ultrasonic welder. Therefore, compared with the case in which no weld boss is provided, the flanges and hub can be welded together more firmly.
In the second aspect of the present invention, a gap may be formed between the outer circumferential surface of the collar and the hub and an inner circumferential surface of the flange, so that residue of the first weld boss can run into the gap. According to the second aspect of the present invention, when two members are to be welded, one of the welding surfaces is provided with a projecting weld boss, and the weld boss is fused for welding. By forming the gap between the inner circumferential surface of the flange and the outer circumferential surface of the collar of the hub, and allowing the residue from the welding surface to run into the gap, the residue of the welding can be prevented from running over onto the surface of the flange.
In the second aspect of the present invention, a gap may be formed between a wall surface of the stepped portion and an outer circumferential surface of a boss provided at an inner circumferential portion of the flange, so that residue of the second weld boss can run into this gap.
In the second aspect of the present invention, instead of the first weld boss, a third weld boss may be provided at a stepped portion cut into the outer circumferential surface of the hub, and an upper surface of the flange may make surface contact with a ceiling portion of this stepped portion. In this structure, a gap is formed between a wall surface of the stepped portion and an inner circumferential surface of the flange, so that residue of the third weld boss can run into this gap. Thus, edges of the recording tape can be prevented from coming into the gap.
In a third aspect of the present invention, a recording tape cartridge rotatably accommodates a reel on which a recording tape is wound. The reel includes a core. An annular lower flange is integrally molded with the core and positioned at one end side of the core.
Outside the core, a cylindrical hub, on which the recording tape is wound, is disposed and fixed at the lower flange. Further, an upper flange is fixed at the other end side of the core, and the upper flange and lower flange held width-directional ends of the recording tape wound on the hub.
By disposing the hub outside the core and winding the recording tape on the hub, even if the core becomes inclined due to thermal contraction after the molding of the core and the lower flange, the inclination of the core does not affect winding of the recording tape, and a highly accurate hub can be obtained.
In the third aspect of the present invention, the hub may include a sleeve attached at an annular depression formed in the lower flange on a concentric circle thereof. During thermal contraction after molding, the thermal contraction is effected along radial directions of the core and the lower flange. Therefore, the annular depression follows the thermal contraction of the core and the lower flange. By providing the annular depression on a concentric circle of the lower flange, and fitting the sleeve in the annular depression, the axis of the sleeve is aligned with axes of the core and the lower flange. Therefore, the axis of the sleeve does not deviate with respect to the lower flange.
In the third aspect of the present invention, a small diameter portion may be provided at one end side of the sleeve, and the small diameter portion may be attached to the annular depression. In this structure, a shoulder portion between the small diameter portion and a large diameter portion abuts on the lower flange. Therefore, even if there is a gap formed between the small diameter portion and the annular depression, the recording tape will not come into the gap.
In the third aspect of the present invention, the sleeve of the hub is inserted in a metal mold for molding the core and the lower flange. Thus, labor for attaching the sleeve after the molding of the core and the lower flange can be saved. Therefore, production steps can be reduced, thereby reducing production costs.
In the third aspect of the present invention, a metal sleeve may be used. Since metals have a lower coefficient of linear expansion than synthetic resins, use of the metal sleeve provides a highly accurate hub.
In the third aspect of the present invention, engaging portions for engaging with the upper flange and the lower flange may be provided at the sleeve at an inner circumferential surface side thereof. In this structure, the recording tape is wound only on the sleeve. Therefore, even if size is irregular at engaged portions of the upper flange and the lower flange which engage with the sleeve, this irregularity does not affect the winding of the recording tape.
In a fourth aspect of the present invention, the reel includes a hollow hub on which recording tape is wound, and annular flanges are disposed at both ends of the hub for holding the width-directional ends of the recording tape wound on the hub. A reel rotation gear is disposed at one end of the hub, and a plate is disposed inside the reel rotation gear, which plate can be attracted by a magnet disposed at a drive for writing/reading information on/from the recording tape.
A braking gear is provided at an outer circumference of one flange, and the braking gear can engage with a braking member disposed in a case that accommodates the reel. By providing the braking gear at the outer circumference of the flange to effect braking, unintended rotation of the reel when the recording tape cartridge is not in use can naturally be prevented with certainty. Further, compared with a case in which the braking gear is provided at a core side of the flange, required braking force is smaller and pitch of the braking gear can be increased. Therefore, failures such as breakage of the braking gear will not be caused. Moreover, since the braking gear is not provided at the core side of the flange, molding accuracy of the reel can be improved.
In the fourth aspect of the present invention, the braking member is urged by an urging device in a direction in which it engages with the braking gear. At a time when a driving gear, which is disposed at the drive and can mesh with the reel rotation gear, meshes with the reel rotation gear, the braking member is pushed in a direction against the urging device to release engagement between the braking member and the braking gear.
In other words, when the driving gear is not meshed with the reel rotation gear, the braking member urged by the urging device engages with the braking gear to block rotation of the reel. On the other hand, at the same time as the driving gear meshes with the reel rotation gear, the braking member is pushed in the direction against the urging device to release engagement between the braking member and the braking gear. Therefore, driving force from the driving gear can be transmitted to the reel rotation gear to rotate the reel.
In the fourth aspect of the present invention, the pitch of the braking gear may be in a range from 1 mm to 3.5 mm. As a result, the braking gear is not easily broken.